Voltage issues

[kf123]

Alright I need some help figuring out this voltage issue I imagine someone here has had a similar problem. Well the other day I bought new batterys because my truck was starting hard... so that was the begining of the problem, put in the new batterys and it started perfect, loved it. on my marry way I go, then about 2 days later the alternator stops charging... at night of all times, but luckily I bought those new batterys so I have enough juice to get home and get to the garage, thinking its the alternator I took it off and brought it to the auto store where they tested it and said it was fine, so I then hooked up and external voltage regulator since I heard the ones in the pcm are junk. got that all hooked up and working and now I am getting wayyyy to much charge, I mean its not at the 18 but i wana say its like 15.5 or so and the airbag light keeps dinging on every once and a while. I am thinking just buy a new alternator? is there somthing inside of them that goes bad, i thought the only regulator was the one in the pcm

[Austin The DieselTech]

Have you check the alternator wiring for any corrosion?  15.5 is a little bit up there.  I usually like to see around 14 volts.

[pctgreg]

What are you using to measure voltage?  How did you wire in the voltage regulator?

[Kilch123]

The first thing I would do is disconnect both batteries and test them separately.  One could be shorted and sending a "need charge" signal, but the other is fully charged

[kf123]

Ok got the problem fixed, it acctually was the alternator. Put a diffrent one on today and everything worked great... took my old one back into advance to have them test it again and this time it said fail... somthing must of just been going bad and didnt register on the machine the last time I had them test it. and yea i did wire the regulator in correctly it is all working good now. I had a feeling it was the alternator, everyone I talked to though said it couldnt be. its running at about 14.2 volts now